This invention relates to a membrane horn switch assembly for a driver side supplemental inflatable restraint (SIR) system. Driver side SIR systems typically include an air bag stored in a housing module. SIR systems are designed to actuate upon sudden deceleration so as to rapidly deploy an air bag in order to restrain the movement of the driver. A driver side SIR system is normally positioned under a steering wheel cover within a hub of a steering wheel. Traditionally, this is where a membrane horn switch is also located. Driver side SIR systems have therefore been adapted to include the membrane horn switch.
Driver side SIR systems are conventionally mounted on the steering wheel along with the membrane horn switch. As is known, the membrane horn switch generally comprises a dielectric substrate, a flexible membrane extending parallel to the substrate and a separator that is inserted between opposing surfaces of the membrane and the substrate. Circuit conductors are provided on the opposing surfaces of the membrane and the substrate. Pressure on the membrane horn switch pushes the conductors together to close a horn circuit that the membrane horn switch is connected to in order to actuate a remote horn. When the flexible membrane that carries the movable contact is deformed, it moves towards a fixed contact on the substrate and upon physically touching the fixed contact, the electrical switch connection is made and the horn is actuated. Upon release of the pressure, the circuit is broken and the horn is silenced.
Membrane horn switches require some form of a rigid base to be compressed against. Having the SIR system and the membrane horn switch located within the steering wheel hub calls for the components that make up the SIR system and the membrane horn switch to be tightly packed. When the membrane horn switch is tightly packed between a folded air bag cushion and the steering wheel cover, it is susceptible to inadvertent actuation. This inadvertent actuation could occur with a minor accidental bumping of the steering wheel cover or with a temperature related compression on the steering wheel cover caused by the expansion or contraction of the integrated parts due to extremes in temperature. For example when the temperature is very cold, the steering wheel cover could contract without any pressure exerted on it by the vehicle driver. The temperature related contraction of the steering wheel cover would therefore cause the switch to react in the way it responds when the driver exerts pressure on the steering wheel cover. In other words, the horn will sound because the conductive surfaces on the substrate and the flexible membrane are forced together to complete the horn circuit. However, unlike actuation of the horn by hand pressure, the contraction that takes place due to the extreme cold temperature causes the horn switch to remain in the contracted position in which the conductive surfaces are in contact until the temperature rises causing the cover to expand to its original position in which the conductive surfaces are separate from one another. This results in the constant sound of the horn in cold temperatures.
Another consideration in designing membrane horn switches is the amount of pressure needed to actuate the membrane horn switch. It is therefore desirous to have a membrane horn switch that can be activated with a consistent minimal pressure. However, orienting the conductive surfaces close together as is needed for minimal contact actuation also has the added risk of the unintentional closing of the circuit or sounding of the horn. Accordingly, in order to ensure that the conductive surfaces are not so close as to accidentally activate the switch, the conductive surfaces of the conventional membrane horn switches are spaced further apart so that a greater amount of pressure on the steering wheel cover is needed to force the conductive surfaces together closing the circuit and thereby actuating the vehicle horn.
It is therefore desirable to provide a dual contact membrane horn switch assembly that when exposed to extremes in temperature will not trigger actuation of the switch and thereby sound the vehicle's horn. In addition, it is desirous to provide a dual contact membrane horn switch assembly which requires consistent minimal pressure to close the circuit and thereby actuate the vehicle's horn.